The growing very dangerous threat from increasingly mean and lawless people willing to destroy democracy and de-power the vote to get their way.

What's happened to many great candidates makes perfect sense if electability is ruling this time. That's especially true among minority voters who face potential loss of all gains over the past several decades. They're already feeling the effects of courts increasingly being packed with authoritarian RW bigots and religious ideologues. Women's and LGBTQ rights are also threatened, and women alone are half of AA after all.

VP Biden was already far out ahead of everyone, and already well liked by many AA, before he even entered the race, and he's stayed there. My guess is Senator Harris's only chance was to magically come from way behind to soar out ahead of Biden, or at least strongly challenge, and stay there.

Same for Booker and all the other redoubtable, dynamic candidates whose calls have gone unanswered by the electorate because they weren't able to prove electability up front. This time.

And all the other reasons being cited are secondary at best to recognition by people who have both feet on the ground that we are living in very dangerous times.